BEIJING, Sept 27 (Reuters) - China on Thursday criticized the United States for flying B-52 bombers in the vicinity of the South China Sea, and demanded that the U.S. take steps to improve military relations amid heightened tensions between the two countries.

Defence ministry spokesman Ren Guoqiang told a monthly briefing that China is resolutely opposed to provocative U.S. military actions in the South China Sea - where China, Taiwan, Vietnam, Malaysia, Brunei and the Philippines have rival claims.

Separately, Foreign Ministry spokesman Geng Shuang denied U.S. President Donald Trump’s accusation that Beijing is trying to influence the U.S. congressional elections in November.

“We advise the United States to stop this unceasing criticism and slander of China,” Geng said at a briefing in Beijing.

“Stop these wrong words and deeds that damage bilateral relations and the basic interests of both countries’ peoples,” Geng said.

The two countries, already engaged in an acrimonious trade war, continue to butt heads over a list of sensitive issues including the South China Sea and Taiwan.

On Saturday, China summoned the U.S. ambassador in Beijing and postponed joint military talks to protest Washington’s decision to sanction a Chinese military agency and its director for buying Russian fighter jets and a surface-to-air missile system.

Beijing has also denied a request for a U.S. warship to visit Hong Kong, the U.S. consulate in the Chinese city said on Tuesday.

China also expressed anger after the U.S. approved the sale of spare parts for F-16 fighter planes and other military aircraft worth up to $330 million to self-ruled Taiwan, which China considers a renegade province. (Reporting by Ben Blanchard and Christian Shepherd; Writing by Se Young Lee; Editing by Darren Schuettler)